Eur J Cardiothorac Surg 2004;25:196-202
© 2004 Elsevier Science NL
Cardiac complications during waiting for elective coronary artery bypass graft surgery: incidence, temporal distribution and predictive factors
Fernando Henpin Yue Cesena*,
Desiderio Favarato,
Luiz Antônio Machado César,
Sérgio Almeida de Oliveira,
Protásio Lemos da Luz
Heart Institute (InCor), University of São Paulo Medical School, Av. Dr Enéas de Carvalho Aguiar, 44 São Paulo, SP 05403-000, Brazil
Received 7 July 2003;
received in revised form 5 November 2003;
accepted 10 November 2003.
* Corresponding author. Tel.: +55-11-30695352; fax: +55-11-30695447
e-mail: fycesena{at}usp.br
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Abstract
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Objectives: Since waiting lists for coronary artery bypass graft surgery are common and carry a risk of severe events, the purposes of this study were: (1) to analyse the incidence and temporal distribution of cardiac complications during waiting for elective coronary artery bypass grafting; (2) to identify predictive factors of such complications. Methods: Data were collected from 574 patients referred to surgery from 1 January 1998 to 12 July 2001. Two types of complications were defined: (1) a composite end-point, which included cardiac death, myocardial infarction, unstable angina or hospital admission due to cardiac cause; (2) sudden or any cardiac death. Previous cardiac events, risk factors, clinical features, laboratory exams, non-invasive tests for myocardial ischemia, left ventricular function and coronary anatomy were analysed. Kaplan–Meier method, multivariate Cox regression and Student's t-test were used for statistical analyses. Results: Median time to surgery was 126 days (5–1022). Among 516 patients consecutively referred to the surgery from 1 January 1998 to 31 December 2000, sudden or cardiac death occurred in 2.5% and the composite end-point in 22.9%. Most complications (72.1%) were observed within 120 days. The main factors predictive of sudden or cardiac death were severe left ventricular dysfunction and heart failure (univariate analysis). Independent predictive factors of the composite end-point were angina, heart failure functional classes and high triglyceride levels. Conclusions: During long delay for coronary artery bypass surgery, cardiac events are frequent and tend to occur early. Severe left ventricular dysfunction, advanced angina, heart failure functional classes and high triglyceride level must be considered when selection is necessary, in order to diminish morbidity and mortality during the waiting period.
Key Words: Coronary disease • Coronary artery bypass • Waiting lists
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1. Introduction
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Waiting lists for coronary artery bypass graft surgery (CABG) are unavoidable in countries that provide universal access to health care and such delay may cause several undesirable events. For instance, severe cardiac complications may occur during the waiting period and the risk of death increases as the delay is prolonged [1–8]. In addition, hospital new admissions add costs to health systems. Since many patients are referred to surgery at economically active age, waiting not only diminishes productivity but also overcharges government spending. Psychological stress due to prolonged waiting interferes in quality of life, predisposing patients to depression and anxiety [8,9]. Furthermore, mental stress triggers myocardial ischemia [10], which may have particular importance in these high-risk patients.
Hence, knowledge of factors associated with complications may help to optimize patients' selection and reduce morbidity and mortality during the waiting period.
Accordingly, the purposes of this study were: (1) to analyse the incidence and temporal distribution of cardiac complications during the waiting for elective CABG; (2) to identify predictive factors of such complications.
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2. Material and methods
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From 1 January 1998 to 12 July 2001, 596 patients were scheduled to elective CABG at Heart Institute (InCor), University of São Paulo Medical School, Brazil. This list did not include patients affected by valve disease requiring surgical correction independently of coronary artery disease, but possibility of CABG combined with ventricular reconstruction was accepted. The therapeutic choice was reconsidered during the waiting period in 22 patients, who crossed over to PTCA/stenting (10 patients) or medical treatment (12 patients). The remaining 574 individuals composed the study group.
Patients were followed in the setting of a specialized Coronary Artery Disease Ambulatory. Clinical evaluation and laboratory assessment periodicity, as well as medication prescription, were left to the attending physician's discretion. The authors did not interfere in the usual selection criteria used to schedule surgeries, which included anginal status, coronary anatomy, ischemia at non-invasive tests and left ventricular function. The study was approved by the institutional Ethics Committee.
Data were collected by a single researcher (FHYC) through interviews and analysis of medical records. Time for surgery or complication was always considered from the moment of referral to surgery. Two types of complications were defined: (1) a composite end-point, which included sudden or any cardiac death, myocardial infarction, unstable angina or hospital admission due to cardiac cause for at least 24 h; (2) sudden or any cardiac death.
The following prognostic factors were analysed: sex, age (at the moment of referral), previous cardiac events, i.e. myocardial infarction, unstable angina, percutaneous transluminal coronary angioplasty (PTCA) and CABG; risk factors, i.e. systemic arterial hypertension, diabetes mellitus, obesity and overweight; angina, heart failure functional classes (at the moment of referral, according to New York Heart Association); physical examination including arterial blood pressures and body mass index (BMI); laboratory exams, i.e. plasma lipids, fasting glucose and creatinine; non-invasive tests for myocardial ischemia; left ventricular systolic function; and coronary anatomy.
Arterial hypertension was considered in the presence of anti-hypertensive medication or at least three readings equal to or higher than 140/90 mmHg. Diabetes mellitus was considered in the presence of hypoglycemic drugs or at least two fasting plasma glucose levels of 126 mg/dl (6.99 mmol/l) or higher. Obesity and overweight were defined as BMI equal to or higher than 30.0 kg/m2 and between 25.0 and 29.9 kg/m2, respectively. Data regarding physical examination and complementary exams were considered from the moment of referral to surgery until the first cardiac event or the surgery, if no complication occurred. For a single patient, mean value of a variable was considered if it was assessed more than once during the waiting.
High risk ischemia at non-invasive tests was considered if at least one of the following features was present:
- at exercise EKG testing: ST depression higher than 0.2 mV if upsloping or equal to or higher than 0.2 mV if horizontal or downsloping, ST depression of at least 0.1 mV in the first stage or persistent ST depression after 5 min of recovery;
- at perfusion scintigraphy: multiple reversible perfusion defects, extensive reversible perfusion defect, transient left ventricle dilation after stress or increased lung thallium-201 uptake after stress;
- at stress echocardiogram: transient motility alterations suggestive of ischemia in multiple walls, corresponding to more than one vascular supply region, extensive transient motility alteration and reversible left ventricle dilation after stress.
Left ventricular systolic function was assessed by ventriculography during cardiac catheterization before referral to surgery and by transthoracic echocardiogram. At ventriculogram, left ventricular systolic function was graded according to the Coronary Artery Surgery Study (CASS) [11]. Normal function was considered if the score was 5 or 6; mild dysfunction was considered if the score summed 7–9, moderate if 10–12 and severe if above 12.
Coronary lesions were classified as proposed by CASS [11]. The number of diseased vessels and proximal lesions were analysed. Coronary anatomy was also divided into five categories, as defined by Ontario score [12]: left main disease; multivessel including proximal anterior descendent artery stenosis; three-vessel without anterior descendent artery stenosis; single-vessel proximal anterior descendent artery stenosis; and one or two-vessel disease without anterior descendent artery lesion.
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3. Statistical analyses
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For identification of predictive factors of complications, patients were first categorized into two groups for each variable. For age, two analyses were performed, categorizing patients above or below 60 and 70 years. For angina and heart failure functional classes, patients were divided into class I or II and class III or IV. For total and LDL-cholesterol, analyses were performed with two cut off points: 200 and 240 mg/dl (5.18 and 6.22 mmol/l) for total cholesterol, and 130 and 160 mg/dl (3.37 and 4.14 mmol/l) for LDL-cholesterol. Cut off points for HDL-cholesterol and triglyceride were 40 and 150 mg/dl (1.04 and 1.70 mmol/l), respectively. For fasting glucose, two cut off points were defined (110 and 126 mg/dl [6.11 and 6.99 mmol/l]) and for creatinine the level chosen to categorize patients was 1.5 mg/dl (132.6 µmol/l). For ischemia in non-invasive tests, two analyses were done: for patients with or without any ischemia, and those with or without high-risk ischemia. For left ventricular systolic function, patients were categorized as with or without severe dysfunction, at ventriculogram or echocardiogram. For coronary anatomy, patients were separated into those with or without three-vessel disease, with or without two or three proximal coronary lesions and with or without main left disease or multivessel including proximal anterior descendent artery stenosis.
Univariate analyses were performed by Kaplan–Meier product limit method; curves were compared by log-rank test. The time for the first event was considered. For censored cases, that is, when no complication was observed, it was considered the waiting time for surgery, the time until the patient was withdrawn from the waiting list due to any cause, or the time between referral to surgery and the last ambulatory evaluation (when the patient was waiting for the surgery at 28 February 2002, when the authors stopped collecting data).
Variables associated with complications at univariate analyses with a level of significance (P) lower than 0.20 were selected to compose a Cox multivariate regression model, when a P-value lower than 0.05 was considered significant.
Comparisons between means were done by Student's t-test for two independent groups.
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4. Results
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4.1. Patient characteristics, follow-up and waiting time
The baseline characteristics, as well as laboratory data collected and medication prescribed during the waiting period, are shown in Table 1. Patients were characterized by a high frequency of risk factors. Anti-hypertensive drugs were prescribed to 99.6% of hypertensive patients; oral hypoglycemic agent and insulin were recommended to 64.6 and 15.3% of diabetic patients, respectively. Statins were prescribed to 55.8% of patients with total cholesterol 240 mg/dl or greater and 57.5% with LDL-cholesterol 160 mg/dl or greater, while fibrates were recommended to only 10.3% of individuals with triglycerides 200 mg/dl or higher and 7.5% with HDL-cholesterol below 40 mg/dl.
Among the 574 patients enrolled in the study, the great majority (505 or 88.0%) had been subjected to surgery at the end of the study, 12 patients (2.1%) died while waiting, 2 patients (0.3%) were withdrawn from the waiting list after stroke, 26 patients (4.5%) refused operation, 3 patients (0.5%) were still awaiting surgery when data collection was stopped and in 26 patients (4.5%) the follow-up information could not be obtained.
Waiting time for surgery ranged from 5 to 1022 days; the mean time±SD was 170±159 and the median time was 126 days.
4.2. Incidence and temporal distribution of events
The incidence of cardiac events was calculated on 516 patients referred to surgery consecutively from 1 January 1998 to 31 December 2000. Cases from 2001 were not consecutive and were excluded from this analysis to avoid bias. Sudden or cardiac death occurred in 12 patients (2.5%, excluding missing data), non-fatal ST elevation myocardial infarction in 5 patients (1.1%), unstable angina or non-fatal non-ST elevation myocardial infarction in 87 patients (18.7%) and hospital admission due to cardiac cause for at least 24 h in 93 patients (20.0%). The composite end-point was observed in 107 patients (22.9%).
The probability of being free of complications during the waiting time is shown in Fig. 1
. The time for the first composite end-point ranged from 1 to 597 days (mean±SD, 109±125). Forty-eight percent of complications occurred within 60 days and 72.1% within 120 days of waiting. Sudden or cardiac death was observed from 14 to 597 days of waiting (mean±SD, 247±221; median, 222 days).
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Fig. 1. Estimated cumulative event free probability during the waiting period. *Composite end-point included sudden or cardiac death, myocardial infarction, unstable angina or hospital admission due to cardiac cause for at least 24 h.
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4.3. Predictive factors of the composite end-point
All 574 patients were included in the analyses for identification of predictive factors of complications. At univariate analysis, 11 variables were related to the composite end-point with a level of significance lower than 0.20 (Fig. 2)
. After Cox multivariate regression, angina class III or IV, heart failure class III or IV and triglyceride levels equal to or higher than 150 mg/dl (1.70 mmol/l) were independently associated with the composite end-point (Fig. 3)
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Fig. 2. Factors associated with the composite end-point at univariate analysis. HF, heart failure; UA, unstable angina; PTCA, percutaneous transluminal coronary angioplasty; TG, triglyceride; DBP, diastolic blood pressure; CABG, coronary artery bypass graft surgery; MI, myocardial infarction.
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Fig. 3. Estimated cumulative free probability of the composite end-point according to angina functional class (A), heart failure functional class (B, both at the moment of referral to surgery) and triglyceride level (C). HR, hazard ratio; CI, confidence interval; HF, heart failure; TG, triglyceride.
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Age, blood pressure, BMI, lipids, fasting glucose and creatinine levels and left ventricular ejection fraction were compared between patients with and without the composite end-point (Table 2). Only HDL-cholesterol levels were significantly different between the groups, lower in those who had some complication.
4.4. Predictive factors of sudden or any cardiac death
At univariate analysis, the following variables were related to sudden or cardiac death: previous extensive anterior myocardial infarction (hazard ratio [HR] 13.16, P<0.01), heart failure class III or IV (HR 6.85, P<0.01), severe systolic left ventricular dysfunction (HR 5.62, P<0.01), referral to surgery within two months post-myocardial infarction (HR 4.26, P=0.02), obesity (HR 3.72, P=0.04) and total cholesterol equal to or higher than 240 mg/dl (6.22 mmol/l, HR 3.68, P=0.04). The small number of deaths did not allow a multivariate analysis.
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5. Discussion
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The main findings of this study were: (1) cardiac events were frequent and tended to occur early during waiting for elective CABG; (2) left ventricular dysfunction and heart failure were the main factors related to sudden or cardiac death; (3) angina and heart failure functional classes and triglyceride levels were independent predictors of the composite end-point.
Mortality rate (2.5%) of this study is comparable to that observed by the majority of other reports, ranging from 0.4 to 4.0% [1–7]. Importantly, the mortality rate is highly correlated with waiting time (Fig. 4)
. Despite representing the minority of complications, these deaths must not be underestimated, since they were potentially avoidable.
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Fig. 4. Correlation between waiting time for CABG and mortality during the waiting in the present study (arrow) and other correlated reports [1–8].
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The rate of non-fatal myocardial infarction (1.1%) is similar to that described by Koomen et al. [1] (1.9%) and by Bengtson et al. [13] (1.7%), who studied patients awaiting PTCA or CABG. Jackson et al. [5], in New Zealand, reported a higher proportion of non-fatal myocardial infarctions (6%) and readmissions due to unstable angina (34 versus 18.7% in the present study), in a sample that included 20.7% of ‘acute cases’ and with a marked delay for the surgery, i.e. median 212 days for elective cases. On the other hand, Seddon et al. [6] described an incidence of deaths, non-fatal myocardial infarctions or cardiac readmissions lower than our composite end-point (10 versus 22.9%), in conditions with similar waiting times.
Comparisons between incidences of complications among different studies are limited by several factors, such as population characteristics and waiting time. In general, our sample was characterized by a higher proportion of risk factors, previous myocardial infarction and severe left ventricular dysfunction, compared to population of similar reports [1,3–6]. It is noteworthy that only elective cases were included in the present study, whereas urgent and elective patients composed the study population of other publications [1,3,4–6].
Another relevant observation is that most complications occurred in the initial months of waiting, namely 72.1% within 120 days, while less than half of the surgeries were performed in the same period. Other studies [1–4] also documented similar findings. This observation deserves attention during the selection process for operations.
We attempted to identify predictive factors of complications, which may help the establishment of priorities and management of waiting lists. Our results emphasize the importance of left ventricular dysfunction and heart failure, which is in accordance with other studies [3,13]. Moreover, the need to consider left ventricular dysfunction in selection is corroborated by evidence of a direct relationship between early revascularization and myocardium functional recovery. Beanlands et al. [14], analysing 35 patients with left ventricular ejection fraction equal to or lower than 35%, noted that individuals who waited less than 35 days showed improvement in left ventricular ejection fraction after 3 months, while those who waited more than 35 days did not.
High grade angina was also an important risk factor for complications, reflecting anatomical and/or pathophysiological conditions, with more extensive disease and/or more vulnerable plaques. The prognostic relevance of angina status was also demonstrated in a number of studies [15–17]. Califf et al. [16] reported that a score based on angina features and ST/T segment changes was an independent predictor of worse prognosis. Similarly, an angina score independently predicted mortality and admission due to acute coronary syndrome in outpatients with coronary artery disease in a study of Spertus et al. [17]. Angina class III or IV and unstable angina three months before indication for CABG were also related to cardiac events in reports focusing the waiting period [1,6].
We found an independent relationship between high triglyceride levels and events, which can be explained by several pathophysiological mechanisms [18–21]. Importantly, high triglyceride concentration is a component of the metabolic syndrome, strongly related to cardiovascular morbidity and mortality [22]. In particular, high triglyceride is associated with low HDL-cholesterol and a greater proportion of small dense LDL-cholesterol [23,24], both favoring atherosclerotic process. In this study, although HDL-cholesterol was not independently related to events, mean HDL-cholesterol level was significantly lower in patients who presented the composite end-point, compared to those who did not. However, while triglyceride concentrations were obtained in 88.2% of the individuals, HDL-cholesterol was assessed in only 54.5% (Table 1), and this difference may have accounted for the results, favoring the appearance of triglyceride, and not HDL-cholesterol, as independent predictor of events. Interestingly, the present results closely resemble those of Chester et al. [25], in which high triglyceride levels, unstable angina and young age were independently related to adverse events in men awaiting routine PTCA.
The absence of association between arterial hypertension, diabetes mellitus, high total and LDL-cholesterol, coronary anatomy and ischemia at non-invasive tests with events in the present study must not be considered a contradiction to the ample evidence linking these factors to prognosis in coronary artery disease. Actually, the results only showed that they were not important to the prognosis of a highly selected population during a short period of time. Furthermore, many severely symptomatic patients were not subjected to non-invasive tests. In addition, coronary anatomy was analysed only as the number and location of stenosis; it is possible that a more specific evaluation of plaque morphology would proportionate different results.
In regard to risk factors effects, almost all of them—with the exception of triglycerides and HDL-cholesterol—were not related to complications, although their control was suboptimal during the waiting (Tables 1 and 2). Medication effects may have lessened the influence of risk factors. Interestingly, while most patients with arterial hypertension, diabetes mellitus and important LDL-cholesterol elevation were treated with some specific medication, fibrate was prescribed only to a minority of individuals with high triglyceride or low HDL-cholesterol levels. It must be emphasized that most of the study was conducted before recent guidelines on lipid management and economic concerns certainly limited correct medication use.
5.1. Limitations
One limitation of the study refers to the proportion of missing data in some instances, which may have interfered with some results, as mentioned above for HDL-cholesterol levels. Furthermore, some risk factors such as smoking, menopause, familiar antecedent of coronary disease were not analysed. Another limitation was the small number of deaths, which did not allow multivariate analysis. Finally, race, social-economic conditions, waiting times and even regional medical approach can also limit extrapolation of our results to different populations.
5.2. Implications and conclusions
The study showed that, in conditions of long delay for CABG, cardiac events are frequent and tend to occur early during the waiting. It was possible to identify predictive factors of events, namely severe left ventricular dysfunction, advanced angina, heart failure functional classes and high triglyceride; these features must be considered when selection policies are necessary, in order to diminish morbidity and mortality during the waiting period. Aggressive treatment of elevated triglyceride may be advisable for these high risk patients.
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Top
Abstract
1. Introduction
